Bright tin electrodepositing

ABSTRACT

ACID TIN BATHS FOR ELECTRODEPOSITING BRIGHT TIN COMPRISING TIN IONS, FREE ACID, A NON-IONIC SURFACE ACTIVE AGENT AND AS A BRIGHTENING AGENT A SUBSTANTIALLY LINEAR, LOW MOLECULAR WEIGHT, SOLUBLE POLYMERIC ACROLEIN OR METHACROLEIN. THE POLYMERIC ACROLEIN OR METHACROLEIN IS A HOMOPOLYMER OR COPOLYMER. ADDITIVE COMPOSITIONS FOR ACID TIN ELECTRODEPOSITING BATHS ARE ALSO PROVIDED BY THE INVENTION.

United States Patent 3,694,329 BRIGHT TIN ELECTRODEPOSITING Marcis M.Kampe, Brookline, Mass., assignor to Enthone, Incorporated, New Haven,Conn. No Drawing. Filed July 30, 1970, Ser. No. 59,749 Int. C1. (223!)5/14 US. Cl. 204--54 R 23 Claims ABSTRACT OF THE DISCLOSURE Acid tinbaths for electrodepositing bright tin comprising tin ions, free acid, anon-ionic surface active agent and as a brightening agent asubstantially linear, low molecular weight, soluble polymeric acroleinor methacrolein. The polymeric acrolein or methacrolein is a homopolymeror copolymer. Additive compositions for acid tin electrodepositing bathsare also provided by the invention.

BACKGROUND OF THE INVENTION 1) Field of the invention This inventionrelates to tin electrodepositing and more especially to bright acid tinelectrodepositing baths and to additive compositions for use inelectrodepositing bright tin from acid tin electrodepositing baths.

'(2) Description of the prior art Acid tin electroplating baths forproducing bright tin deposits are disclosed in the prior art ascontaining sulfonate or fluoborate ions, a reducing agent such asFormalin, a non-ionic surfactant, and as brightening agent an aromaticor heterocyclic ring-containing aldehyde wherein the carbonyl group isdirectly attached to the aromatic or heterocyclic ring or an oc-,B-olefinically unsaturated carbonyl compound, such as A-dihydro-o-tolylaldehyde, A -dihydrobenzaldehyde, cinnamaldehyde,a-ethyl cinnamic acid aldehyde, 2,4-hexadienal, 3-forrnyl, 5,6-dihydro2,6 dimethylpyrane, benzalacetone, benzalacetophenone,2-benzalcyclohexanone, vinyl-phenylketone, p-chlorobenzalacetone,Z-cinnamylthiophene, 2-(w-acetyl)-vinylfurane,2-(w-benzoyl)-vinylfurane, p Cl phenylstyrylketone,isobutylstyrylketone, w-acetyl cinnamic acid ethyl ester andp-tolylstyrylketone. The addition to acid tin electroplating baths ofacrolein per se resulted in no brightness being imparted to the tinelectrodeposits. Further the strong lachrymatory and irritatingproperties of acrolein as well as the toxic nature of this compoundmakes it difiicult to work with.

Acid tin electroplating baths producing bright tin deposits are alsodisclosed in the prior art as containing sulfate, sulfonate orfluoborate ions, a non-ionic surface active agent, as primary brighteneran olefinically unsaturated organic carbonyl compound selected fromthose disclosed immediately supra, and as secondary brightener apolymerizable organic compound capable of reducing the overvoltage forthe evolution of hydrogen at a tin cathode such as acrylic acid,methacrylic acid, acrylioamide, methacrylicamide, glycidylacrylate,propylene glycolacrylate, dimethylaminoethylmethacrylate, glyoxal,glutaric dialdehyde, oz hydroxyadip-icaldehyde, N-vinylpyrolidone,p-diethylaminobenzaldehyde, N vinylcarbazole, 2-vinylpyridine,tetra-hydrofuran, vinyl acetate, and alkylglycidyl ether.

Acid bright tin electroplating baths are also known in the prior artwhich contain a primary brightener of the Formula X-CH=CH--Y wherein Xis phenyl, furfuryl or pyridyl and Y is hydrogen, formyl, carboxyl,alkyl, hydroxyalkyl, formylalkyl, or the acyl radical of a carboxylicacid. Formaldehyde and certain imidazoline derivatives serve assecondary brighteners in such baths, especially when employed withnon-ionic wetting agents.

BRIEF SUMMARY OF THE INVENTION In accordance with the present invention,bright tin electrodeposits are obtained by utilizing as a brighteningagent in otherwise conventional aqueous acid tin baths a substantiallylinear, low molecular weight, soluble polymeric acrolein ormethacrolein. The polymeric acrolein or methacrolein can be ahomopolymer or copolymer. The bath also comprises tin ions, free acidand a non-ionic surface active agent.

The homoand copolymers of acrolein or methacrolein herein are usually ofmolecular weight in the range of about 300-900. The exact structure ofthe polymers herein is not known. In theory the homopolymers containrecurring aldehyde-containing units of the formula 1 Laaol.

wherein n is the number of such units and R is hydrogen or methyl.

The polymers of this invention are obtained by polymerizing the acroleinor methacrolein monomer in the case of homopolymers, or the acrolein ormethacrolein together with the other copolymerizable reactant orreactants or comonomers in the case of the copolymers, at apolymerization temperature in an aqueous alkaline liquid medium,preferably a dilute aqueous solution of a weak base, for example analkali metal carbonate, e.g. sodium carbonate, potassium carbonate orpotassium bicarbonate. Aqueous solutions of other alkaline materialssuch as, for example, sodium hydroxide, potassium hydroxide ortriethylamine can be utilized for the polymerization in place of theaqueous sodium carbonate, potassium carbonate or potassium bicarbonatesolution. The polymerization is commenced at normal or room temperatureand, if necessary, cooling of the reaction mixture is effected duringthe polymerization. A substantially linear, low molecular weight,soluble polymer is obtained which theoretically, in the case of acroleinand methacrolein homopolymers, has the formula:

wherein n is the number of repeating units and R is hydrogen or methyl.Actually the number of aldehyde groups is such polymer molecule is low,and is believed to be only about 15% to 20% of theory. The low aldehydecontent of the polymers is believed due to the conversion of such groupsto ether, hydroxyl or ester linkages and, at times, to aldol.

The polymers of this invention whether homopolymers or copolymers aresoluble in common organic solvents, for example 1-3C alkyl alcohols,methyl ethyl ketone, and acetone and also in dimethyl formamide.

More specifically, in the preparation of the polyacrolein homopolymer,water is introduced into a reaction vessel and acrolein added to theWater therein while stirring the mixture employing magnetic stirring tokeep the ingredients in motion. The acrolein is added slowly to thewater. The alkaline material, e.g. the weak base such as, for instancesodium carbonate or potassium carbonate is then added to the mixture inthe reaction vessel with continued stirring of the mixture. A primaryamine, for

thermic heat of reaction by any suitable indirect cooling means, forinstance a water jacket. The reaction mixture is contained in thereactor for a period sufiicient to allow the polyacrolein to form,typically about a two hour period. The polyacrolein is then separatedfrom the aqueous phase, for instance by decanting, and the polyacroleinthen usually washed with water. The polyacrolein is then usuallydissolved in a water-miscible organic liquid solvent, for exampleisopropanol. Alternatively the alkaline material such as the weak base,e.g. sodium carbonate or potassium carbonate can be added to the aqueousliquid, and then the acrolein and primary amine added slowly andseparately to the liquid mixture from a dropping funnel. The remainderof the preparation procedure in this alternative embodiment is thatdisclosed immediately above.

The polymethacrolein homopolymer may be prepared by the proceduredisclosed immediately supra for the acrolein homopolymer.

In the preparation of the polymeric acrolein, good ventilation, aspark-proof environment and no open flames are recommended at leastduring the initial stage of the reaction. Similar safety conditions arealso recommended for the preparation of polymeric methacrolein. In thecase of the polymeric acrolein, it is also recommended the reactor beblanketed with nitrogen and that a closed reaction system be employed.

In the preparation of the copolymers of acrolein with the differentcopolymerizable compound or compounds disclosed elsewhere herein, thepreparation procedure employed is very similar to that disclosed supraand the acrolein and the other copolymerizable' compound or compoundscan be added to the water together as a premix or added separately tothe water. In the preparation of the copolymers of methacrolein with thedifferent copolymerizable compound or compounds disclosed elsewhereherein, the preparation procedure is very similar to that disclosedsupra and the methacrolein and the other copolymerizable reactant orreactants can be added to the water together as a premix or addedseparately to the reaction vessel.

The acrolein and methacrolein can be represented generically herein bythe formula R H CH2=( J-(i7=O wherein R is a hydrogen atom or methylradical.

The non-ionic surface active agent herein also imparts brightening tothe tin electrodeposit as well as functioning as a wetting agent toimpart wettability of the polymer. By reason of imparting brightening tothe tin electrodeposit, the non-ionic surface active agent may beconsidered a secondary brightener in this invention. If the non-ionicsurface active agent is considered a secondary brightener, then thepolymeric acrolein or methacrolein is considered to be and designated aprimary brightener herein. However, if the non-ionic surfactant is notconsidered a secondary brightener herein, then the polymeric acrolein ormethacrolein is designated simply a brightening agent.

Additional additives that can be added to the tin electrodepositing ofthis invention are, for example, polyvinylpyrrolidone as a molecularcomplexer, and additional isopropanol to aid solubility of the polymericacrolein or methacrolein. An aromatic primary amine, e.g. morp-toluidine or aniline, can also be added to the tin electrodepositingbath containing the Schiff base-terminated homopolymer or copolymer inaccordance with the preferred embodiments of the invention hereinafterdisclosed and also containing the non-ionic surface active agent,inasmuch as it was found that the separate addition of such aromaticprimary amine to the electrodepositing bath resulted in an appreciablybrighter tin electrodeposit over that obtained from the combination ofthe preferred Schitf base-terminated homopolymer or copolymer and thenon-ionic surface active agent.

The amounts of polymeric acrolein or methacrolein and of the non-ionicsurface active agent added to the tin electro-depositing bath is anamount of each of the polymer and non-ionic surface active agent whichis sufficient to provide a bright tin electrodeposit. The polymericacrolein or methacrolein and non-ionic surfactant are utilizable in theplating baths in amounts that can be varied considerably. Actually onlya small or minor amount of each will sufiice in the bath, with about2-30 ml. of a polymeric acrolein or methacrolein solution of about 10%by weight polymer concentration per liter of bath solution and 230 ml.of non-ionic surface active agent per liter of bath solution givingsatisfactory results. Greater amounts of the polymeric acrolein ormethacrolein can be added to the bath with the upper limit beingdetermined by factors of economy and solubility of the homoor copolymerin the bath, and even somewhat smaller amounts of the polymer can beadded to the bath. Greater amounts of the non-ionic surfactant can alsobe utilized in the bath and somewhat smaller amounts of this surfactantcan also be utilized therein.

The temperature of the tin electrodepositing baths herein during theelectroplating is usually in the range of about 6585 F.

The electroplating baths of this invention provide bright smooth tindeposits over a fairly wide range of current densities, which may rangefrom low through high current densities, inclusive.

In carrying out the tin electrodeposition, the article or articles onwhich the tin is to be deposited is made the cathode in theelectrodepositing bath of this invention and a direct electrical currentpassed from the anode or anodes through the bath to the cathode.

Any suitable non-ionic surface active agent or surfactant is utilizableherein. The surface active agents are exemplified by Triton N-lOl, anonyl phenol polyether alcohol; Triton X400, an octyl phenol polyetheralcohol and other alkyl aryl polyether alcohols disclosed in thepublication Rohm & Haas Surfactants, Handbook of Physical Properties,published by Rohm & Haas Co., Independence Mall West, Philadelphia, Pa.19105. Additional examples of non-ionic surface active agents utilizableherein are Igepal CO-7l0, Igepal CO-730, Igepal CO-630 and IgepalCO-430, obtainable from the Antara Chemical Company.

The brightener additives of this invention comprise a mixture of thesubstantially linear, low molecular weight. soluble polymeric acroleinor methacrolein, and a watermiscible diluent or carrier therefor. Thediluent or carrier is usually a water-miscible organic liquid solventsuch as, for example, a 1-3C alkyl alcohol, methyl ethyl ketone,acetone, dimethyl formamide, ethylene glycol or glycerine, with thepolymeric acrolein or methacrolein dissolved in the solvent whereby theadditive composition is a solution. The polymer can be a homopolymer orcopolymer as is previously disclosed herein.

The amount of polymeric acrolein or methacrolein in the brighteneradditives herein can be varied over a broad range. Thus the polymericacrolein or methacrolein (homopolymer or copolymer) can be present inthe brightener additive in an amount in the range of about 5 by weightbased on total additive composition. The non-ionic surface active agentmay also be a constituent of the brightener additive of this inventionand when utilized therein, will usually be present in amount within therange of about 10%-60% by weight based on total additive composition.

Alternatively the polymeric acrolein or methacrolein can be added assuch to the acid tin electrodepositing bath but this in not preferred.

The polymeric acrolein or methacrolein of this invention is of low orlimited solubility in the aqueous tin electroplating baths herein but issufficiently soluble in the baths to be effective therein as abrightener.

Copolymers of acrolein or methacrolein and a diiferent copolymerizablecompound or compounds utilizable as brightening agent in the tin platingbaths herein are, for example copolymers of acrolein and methacrolein,copolymers of acrolein or methacrolein and crotonaldehyde, copolymers ofacrolein or methacrolein and formaldehyde, copolymers of acrolein ormethacrolein and acrylamide, copolymers of acrolein or methacrolein andvinyl acetate and copolymers of acrolein, methacrolein and urea. Thecopolymers are preparable by the same polymerization process previouslydisclosed herein for preparing the homopolymers herein and involvingcopolymerizing the comonomers or polymerizable materials in a diluteaqueous alkaline solution as exemplified by a dilute aqueous solution ofpotassium carbonate, sodium carbonate or potassium bicarbonate. Theacrolein-methacrolein copolymers are prepared by copolymerizing theacrolein and methacrolein in a mole ratio of typically about 4:1respectively; the acrolein-crotonaldehyde copolymers are prepared bycopolymerizing the acrolein and crotonaldehyde in a mole ratio usuallyin the molar ratio range of about 1-4:1 respectively; theacroleinformaldehyde copolymers by copolymerizing the acrolein andformaldehyde in a mole ratio usually in the molar ratio range of about4:1 to about 3:2 respectively; the acrolein-acrylamide copolymers bycopolymerizing the acrolein and acrylamide in a mole ratio usually inthe molar ratio range of about 4.9:0.1 to about 4:1 respectively; theacrolein-vinyl copolymers by copolymerizing the acrolein and vinylacetate in :a mole ratio usually in the molar ratio range of about4.9:0.1 to about 4:1 respectively, and the acrolein-methacrolein-ureacopolymers by copolymerizing the acrolein, methacrolein and urea in amole ratio of typically about 4.0:0.8:0.2 respectively. The copolymersof methacrolein and the dilferent copolymerizable compound are preparedby copolymerizing the methacrolein and the different copolymerizablecompound typically in the mole ratios disclosed immediately supra forthe acrolein copolymer preparation with the methacrolein replacing theacrolein, except that in the case of the methacrolein-acroleincopolymers, the methacrolein and acrolein will be copolymerizedtypically in a mole ratio of 4:1 respectively. The exact structure ofthe copolymers herein is not known.

The tin or stannous ions are usually supplied in the plating bathsherein as a water-soluble stannous salt, for example stannous sulfate orstannous fluoborate. The free acid of the baths are exemplified bysulfuric, fluoboric or aromatic sulfonic acid, e.g. benzene sulfonicacid. The tin and free acid concentrations of the baths can be variedover fairly broad limits as is well known in the art, with a tin contentof 15-100 grams per liter (calculated as Sn), and a free acidconcentration of 35-200 grams per liter being typical of the sulfate,fluoborate and aromatic sulfonate baths.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymers utilized asbrighteners in this invention including the homopolymers and copolymersare preferably Schitf base terminated to prevent crosslinking of thepolymer to form an insoluble, three-dimensional resin which isunsatisfactory for use in the tin electrodepositing bath, and also tostabilize the polymer to prevent degradation and decomposition of thepolymer. Additionally the Schiff base terminal group or groups appear tohave another function in the tin electrodepositing baths besides theirpolymer stabilization function and that is to impart brightness to thetin electrodeposit. The Schiif base terminal group or groups of thepolymers are obtained by adding a primary amine as a Schiff baseterminal group precursor to the polymerization (homopolymerization orcopolymerization) reaction mixture, with the resulting condensationreaction between the amine hydrogens and the carbonyl group or groupsoxygen atom or atoms of the polymeric acrolein or methacrolein resultingin the Schifi base terminal group or groups. The Schifl base terminalgroup has the formula wherein R is the remainder of the residue of aprimary amine as is hereinafter defined and can be, for example, anaryl, heterocyclic or aralkyl radical. Any suitable primary amine can bereacted with the aldehyde carbonyl group or groups oxygens in thepolymerization reaction mixture to form the Schiif base terminal groupor groups. When R of the above Schifi base terminal group formula isaryl, exemplary of such aryl radical is phenyl, tolyl, xylyl andnapththyl; when R is a heterocyclic radical, exemplary of theheterocyclic radical is pyridyl; and when R is an aralkyl radical, i.e.an aromatic alkyl radical,

exemplary of the aralakyl radical is benzyl.

The term remainder of the residue of ;a primary amine used herein meansthe remaining portion of the primary amine exclusive of the nitrogenatom and amino group hydrogens after the amino group hydrogens of theprimary amine have reacted with the carbonyl group oxygen of thepolymeric acrolein or methacrolein by a condensation reaction to formthe Schiif base terminal group or groups. Such remaining portion of theprimary amine is, for example, an aryl, heterocyclic or aralkyl radicalas disclosed supra.

Any suitable primary amine is utilizable herein as reactant for formingthe Schiif base terminal group or groups. Exemplary of the primary amineare monoand bicyclic aromatic primay amines, e.g. o-, mand ptoluidines,aniline, xylidines, e.g. 2,3-dimethylaniline, 2, 4-dimethylaniline,2,5-dimethylaniline, 3,4-dimethylaniline and 3,5-dimethylaniline, anda-naphthyl amine, heterocyclic primary amines, e.-g. aminopyridines,e.g. 2-aminopyridine and 3-aminopyridine, and aralkyl amines, e.g.benzyl amine. The primary amine utilized should of course be one that iscapable of stabilizing the polymer or copolymer by the Schiff baseterminal group or groups formation to prevent crosslinking anddecomposition, which all of the above-disclosed primary amines arecapable of doing.

Preferably the Schitf base terminal group or groups, of the polymericacrolein or methacrolein are formed by the condensation reaction of anaromatic primary amine, more preferably aniline or 0-, mor p-toluidine,with the carbonyl group or groups. The Schiff base terminal group orgroups have the following formula when the aniline or o-, morp-toluidine is employed as Schitf base precursor:

wherein R is -CH or --H. o-Toluidine is preferred among the toluidines.

Preferably the primary amine precursor of the Schiff base terminal groupor groups is added to the polymerization reaction mixture in thepreparation of the polymer in a mole ratio of the primary amine to thew, fi-ethylenically unsaturated aldehyde, which is the acrolein ormethacrolein in the case of the homopolymers or the total of acrolein ormethacrolein plus the difierent copolymerizable ethylenicallyunsaturated aldehyde such as, for instance, methacrolein or acroleinrespectively or crotonaldehyde in the case of the copolymers when suchdifferent 0L, B-ethylencially unsaturated aldehyde is thecopolymerizable reactant, in the molar ratio range of about 1:25 toabout 1:75, respectively, more preferably about 1:4 to about 1:6respectively. In the case of copolymers when the diiferentcopolymerizable reactant other than the acrolein or methacroleinutilized in the copolymer preparation is not an w, 5- ethylenicallyunsaturated aldehyde, such mole ratio in the molar ratio range of about1:2.5 to about 1:75, more preferably about 1:4 to 1:6, is of the primaryamine to only the acrolein or methacrolein respectively.

When acrolein is the predominant comonomer in amount, the polymerizationreaction is usually very fast and for this reason the polymerizationtime is preferably in the range from about 20-120 minutes so as to avoidobtaining a polymer which is difiicult to dissolve in an organicsolvent, e.g. isopropanol, and which tends to be produced at longerpolymerization or reaction times.

The polymers of this invention are preferably dissolved in a suitablyorganic liquid solvent, e.g. isopropanol, as soon as possible after thepolymerization is considered completed and substantially immediatelyafter the polymer has been separated from the aqueous liquid of thereaction mixture.

The tin plating baths are preferably sulfate baths wherein the free acidis sulfuric acid and the tin or stannous ions is supplied by stannoussulfate.

The following tests were carried out to evaluate homoand copolymers ofthis invention as brightener additives in acid tin electroplating.

Test Run No. 1

Part A.-To 50 ml. of water at room temperature in a reaction vessel 37.5grams of acrolein (0.67 mole) was added. To this mixture was added 6grams of sodium carbonate and also 13.8 grams of o-toluidine (0.13 mole)as precursor for Schiif base termination of the ultimate polymericacrolein. The reaction mixture was stirred for 20 minutes. The Schiffbase-terminated, substantially linear, low homopolymer of acroleinobtained, which precipitated from the liquid as a yellow resinous solid,was separated by decanting, washed with water, and dissolved in 300 ml.of isopropanol.

Part B.3 ml. of this isopropanol solution of such Schiffbase-terminated, homopolymer of acrolein was added to an aqueous sulfateacid electroplating bath of the following composition:

Stannous sulfate30 g./l. Sulfuric acid--l ml./l. Formaldehyde (37%aqueous solution)7 ml./l.

The sulfuric acid of such bath was of 98% sulfuric acid concentration. 2ml. of an ethoxylated nonyl phenol surfactant was also added to theaqueous sulfate acid tin electroplating bath. Tin plating was carriedout in a Hull test cell under the following conditions: operatingcurrent of 1 and 3 amps, room temperature of the bath, and a platingtime of 5 minutes. The tin electrodeposit on the Hull test panel showedgood brightness over the current density range of -80 a.s.f.

Test Run No. 2

Part A.-A Schiff base-terminated, substantially linear, low homopolymerof acrolein was prepared following a substantially identical preparationprocedure and utilizing the same materials and reactants and quantitiesthereof and reaction conditions employed in Test Run No. 1, Part Aherein, except that 12 grams of aniline (0.13 mole) was utilized in thisTest Run No. 2 instead of the specified amount of o-toluidine utilizedin Test Run No. 1, Part A herein, as Schiff base precursor fortermination of the polymeric acrolein. The Schilf base-terminated,substantially linear, low homopolymer of acrolein obtained was dissolvedin 300 ml. of isopropanol.

Part B.3 ml. of such isopropanol solution of the Schitf base-terminatedhomopolymer of acrolein was added to a sulfate acid tin electroplatingbath of substantially identical composition as utilized in Test Run No.1, Part B herein. 2 ml. of an ethoxylated nonyl phenol surfactant wasalso added to the sulfate acid tin bath. Tin plating was carried out ina Hull test cell under substantially identical conditions of operatingcurrent amperage, bath temperature and plating time as employed in TestRun No. 1, Part -B herein. The tin electrodeposit on the Hull test panelshowed good brightness over the current density range of 10-80 a.s.f.

Test Run No. 3

Part A .-Acrolein in amount of 23.5 grams (0.42 mole) and 23.5 grams ofcrotonaldehyde (0.33 mole) were dispersed in 150 ml. of water at roomtemperature in a reaction vessel. The mixture was agitated vigorouslyand 13.8 grams of o-toluidine (0.13 mole) as Schiff base precursor fortermination of the ultimate acroleincrotonaldehyde copolymer and 6 gramsof sodium carbonate were added thereto. After 20 minutes, a Schitfbaseterminated, substantially linear, low copolymer of acrolein andcrotonaldehyde precipitated from the liquid as a brown resinous solidwhich was separated by decanting, washed with water, and dissolved in300 ml. of isopropanol. I

Part B.3 ml. of this isopropanol solution of Schitf base-terminatedcopolymer of acrolein and crotonaldehyde was added to a sulfate acid tinelectroplating bath of substantially identical composition as utilizedin Test Run No. 1, Part B herein. 2 ml. of an ethoxylated nonyl phenolsurfactant was also added to the sulfate acid tin bath. Tin plating wascarried out in a Hull test cell under substantially identical conditionsof operating current amperage, bath temperature and plating time asemployed in Test Run No. 1, Part B herein. The tin electrodeposit on theHull test panel showed good brightness over the current density range of10-70 a.s.f.

Test Run No. 4

Part A.-To 250 ml. of water at room temperature in a reaction vessel wasadded 37.5 grams of acrolein (0.67 mole) and 10 grams of aqueousformaldehyde (37%). With stirring of the liquid mixture, 4 grams ofsodium carbonate and 13.8 grams of o-toluidine (0.13 mole) as precursorfor Schiff base termination of the ultimate acrolein-formaldehydecopolymer were added thereto. After 20 minutes, a Schiffbase-terminated, substantially linear, low copolymer of acrolein andformaldehyde was obtained, which copolymer was a pale yellow resinoussemi-solid. The copolymer was dissolved in 300 m1. of isopropanol.

Part B.3 ml. of the isopropanol solution of such Schitf base-terminatedcopolymer was added to a sulfate acid tin electroplating bath ofsubstantially identical composition as utilized in Test 'Run No. 1, PartB herein.

2 ml. of an ethoxylated nonyl phenol surfactant was also added to thesulfate acid tin bath. Tin plating was carried out in a Hull test cellunder substantially identical conditions of operating current amperage,bath temperature and plating time as employed in Test Run No. 1, Part Bherein. The tin electrodeposit on the Hull test panel was of goodbrightness over the current density range of 1080 a.s.f.

Test Run No. 5

Part A.To ml. of water at room temperature in a reaction vessel wasadded 40 grams of methacrolein (90%) (0.42 mole). The resulting mixturewas stirred vigorously and 1 gram of sodium hydroxide and 13.8 grams ofo-toluidine (0.13 mole) as precursor for Schiff base termination of theultimate polymeric methacrolein were added thereto. After 20 minutes aSchiif base-terminated, substantially linear, low homopolymer ofmethacrolein precipitated from the liquid as a pale yellow resinoussemi-solid which was separated by decanting, washed with water, anddissolved in ml. of isopropanol.

Part B.3 ml. of the isopropanol solution of such Schilf base-terminatedhomopolymer was added to a sulfate tin electroplating bath ofsubstantially identical composition as utilized in Test Run No. 1, PartB- herein. 2 ml. of an ethoxylated nonyl phenol surfactant was alsoadded to the sulfate acid tin bath. Tin plating was carried out in aHull test cell under substantially identical 9 conditions of operatingcurrent amperage, bath temperature and plating time as employed in TestRun No. 1, Part B herein. The tin electrodeposit on the Hull test panelshowed fair brightness over the current density range of 10-70 a.s.f.

Test Run No.- 6

lart A.To 100 ml. of water at room temperature in 'a reaction vessel wasadded 30 grams of acrolein (0.53 mole) and 7.5 grams. of methacrolein(0.09 mole). 4 grams of sodium carbonate and 13.8 grams of o-toluidine(0.13 mole) as precursor for Schiff base termination of the ultimateacrolein-methacrolein copolymer were added to the resulting mixture.After mixing the thusobtained mixture for 20 minutes, a Schilfbase-terminated, substantially linear, low copolymer of acrolein andmethacroleinprecipitated from the liquid as a' yellow resinoussemi-solid which was separated by decanting, washed with water, anddissolved in 150 ml. of isopropanol.

. Part B. -3 ml. of the isopropanol solution of such Schilfbase-terminated copolymer was added to a sulfate acid tin electroplatingbath of substantially identical composition as utilized in Test Run No.1, Part B herein. 2 ml. of an ethoxylated nonyl phenol surfactant wasalso added to the sulfate acid tin bath. Tin plating was carried out ina Hull test cell under substantially identical conditions of operatingcurrent amperage, bath temperature and plating'time as employed in TestRun No. 1, Part B herein. The tin electrodeposit on the Hull test panelwas of good brightness over the .current density range of 10-60 a.s.f.

' Test Run No. 7

Part A.A Schiff base-terminated, substantially, low copolymer ofacrolein, methacrolein and urea was prepared by a preparation proceduresubstantially identical to that employed in Test Run No. 6, Part Aherein and utilizing the same materials and reactants and quantitiesthereof and reaction conditions as utilized in Test Run No. 6, Part A,except that 7.5 grams of urea as additional reactant or comonomer wasadded to the dispersed acrolein-methacrolein aqueous mixture prior tothe addition of the sodium carbonate" and o-toluidine. The Schiffbase-terminated, substantially linear, low copolymer of acrolein,methacrolein and urea obtained, which was a yellow, resinous semi-solid,was dissolved in 150 ml. of isopropanol.

Part B.-3 ml. of the isopropanol solution of suchacreolein-methacrolein-urea copolymer was added to a sulfate acid tinelectroplating bath of substantially identical composition as utilizedin Test Run No. 1, Part B herein. 2 ml. of an ethoxylated nonyl phenolsurfactant was also added to the sulfate acid tin bath. Tin plating wascarried out in a Hull test cell under substantially identical conditionsof operating current amperage, bath temperature and plating time asemployed in Test Run No. 1, Part B herein. The tin electrodeposit on theHull test panel was of good brightness over the current density range of10-50 a.s.f.

Test Run N0. 8

2 ml. of the isopropanol solution of Schitf base-terminated,substantially linear, low homopolymer of acrolein, prepared inaccordance with Test Run No. 1, Part A herein, was added to an aqueousefluoborate acid tin electroplating bath of the following composition:

g./l. Stannous fluoborate 50 Fluoboric acid (48%) 100 Formaldehyde (37%aqueous solution 10 0.5 ml. of an ethoxylated nonyl phenol surfactantwas also added to the fluoborate acid tin bath. Tin plating was carriedout in a Hull test cell under the following conditions: operatingcurrent of 3 amps; room temperature of the bath; and plating time ofminutes. The tin 10 electrodeposit on the Hull test panel exhibited goodbrightness over the current density range of 10-40 a.s.f.

Test Run No. 9

2 ml. of the isopropanol solution of Schiff baseterminated,substantially linear, low copolymer of acrolein and crotonaldehydeprepared in accordance with Test Run No. 3, Part A herein, was added toan aqueous fluoborate acid tin electroplating bath of a substantiallyidentical composition as that set forth in Test Run No. 8 herein. 0.5ml. of an ethoxylated nonyl phenol surfactant was also added to thefluoborate acid tin bath. Tin plating was carried out in a Hull testcell under substantially identical conditions of operating currentamperage, bath temperature and plating time as employed in Test Run No.8, Part B herein. The tin electrodeposit on the Hull test panel showedgood brightness over the current density range of 1040 a.s.f.

In additional tests carried out utilizing a Hull test cell and astannous sulfate-containing acid tin electroplating bath of acomposition similar to that set forth in Test Run No. 1, Part B herenaddition to the bath of a copolymer of acrolein and vinyl acetatecopolymerized in a mole ratio of 4:1 respectively resulted in a tinelectrodeposit of fair brightness on the test panel. The copolymer ofthe test immediately supra was Schilf base-termined by addition ofo-toluidine to the reaction mixture, and a non-ionic surfactant was alsoadded to the plating bath in the test.

Acrolein per se added separately to a stannous sulfatecontaining acidtin electroplating bath of composition substantially identical to thatset forth in Test Run No. 1, Part B herein resulted in a non-bright tinelectrodeposit on the Hull test panel over the entire current densityrange of the panel. Moreover, its strong lachrymatory property as wellas the toxic and irritating nature of the acrolein made it difficult towork with.

The bright tin electrodepositing of the present invention has utilityfor electrical contacts, electronic component, hardware, and jewelry.The deposits are ductile and submit to soldering operations.

What is claimed is:

1. An aqueous acid bright tin electrodepositing bath comprising tinions, free acid selected from the group consisting of sulfuric,fluoboric and aromatic sulfonic acids, a non-ionic surface active agentand as a brightening agent a substantially linear, soluble Schifibaseterminated polymeric acrolein or methacrolein having a. molecularweight in the range of about 300 900, said non-ionic surface activeagent and said polymeric acrolein or methacrolein each being present ina minor amount suflicient to provide a bright tin electrodeposit.

2. The bath of claim 1 wherein the polymer has been prepared by apolymerization process wherein the mole ratio of a primary amineprecursor of the Schitf base terminal group to 11-, B-ethylenicallyunsaturated aldehyde polymerizable reactant provided in thepolymerization reaction mixture is in the molar ratio range of fromabout 1:25 to about 1:7.5 respectively, the primary amine precursorbeing selected from the group consisting of aromatic primary amines,heterocyclic primary amines and benzyl amine.

3. The bath of claim 2 wherein the Schitf base terminal group of thepolymer has the formula 5. The bath of claim 4 wherein the Schitf baseterminal group is of the formula R wherein R is OH or --H.

6. The bath of claim 1 wherein the free acid is sulfuric acid and thetin ions are supplied by stannous sulfate.

7. The bath of claim 1 wherein the polymeric acrolein is a homopolymerof acrolein.

8. The bath of claim 1 wherein the polymeric methacrolein is ahomopolymer of methacrolein.

9. The bath of claim 1 wherein the polymeric acrolein is copolymer ofacrolein and a different copolymerizable compound.

10. The bath of claim '1 wherein the polymeric methacrolein is acopolymer of methacrolein and a different copolymerizable compound.

11. The bath of claim 9 wherein the dilferent copolymerizable compoundis methacrolein.

12. The bath of claim 9 wherein the different copolymerizable compoundis crotonaldehyde.

13. The bath of claim 9 wherein the different copolymerizable compoundis formaldehyde.

14. The bath of claim 9 wherein the diiferent copolymerizable compoundis acrylamide.

15. The bath of claim 9 wherein the different copolymerizable compoundis vinyl acetate.

16. The bath of claim '1 wherein the polymeric acrolein or methacroleinis prepared by a polymerization process comprising effecting thepolymerizing of the acrolein or methacrolein in an aqueous solution ofan alkaline material selected from the group consisting of an alkalimetal carbonate, sodium hydroxide, potassium hydroxide andtriethylamine.

17. The bath of claim 16 wherein the alkaline material is an alkalimetal carbonate.

18. The bath of claim 17 wherein the alkali metal carbonate is sodiumcarbonate.

19. The bath of claim 17 wherein the alkali metal carbonate is potassiumcarbonate.

20. A method for the electrodeposition of bright tin which comprisespassing an electrical current from an anode through an aqueous acid tinelectrodepositing bath to a cathode on which the tin iselectrodeposited, the bath comprising tin ions, free acid selected fromthe group consisting of sulfuric, fluoboric and aromatic sulfonic acids,a non-ionic surface active agent, and as brightening agent asubstantially linear, soluble, Schifl.

base-terminated polymeric 11-, B-ethylenically unsaturated aldehyde ofthe formula R H CHz=( ](i3=0 wherein R is hydogen or methyl having amolecular weight in the range of about 300-900, said non-ionic surfaceactive agent and said polymeric aldehyde each being present in a minoramount sufficient to provide a bright tin electrodeposit.

21. The method of claim 20 wherein the polymer has been prepared by apolymerization process wherein the mole ratio of a primary amineprecursor of the Schiif base terminal group to 11-, fi-ethylenicallyunsaturated aldehyde polymerizable reactant provided in thepolymerization reaction mixture is in the molar ratio range of fromabout 1:25 to about 1:75 respectively, the primary amine precursor beingselected from the group consisting of aromatic primary amines,heterocyclic primary amines and benzyl amine.

22. The method of claim 20 wherein the Schifi baseterminated polymericaldehyde is prepared by a polymerization process comprising effectingthe polymerizing of the ethylenically unsaturated aldehyde in an aqueoussolution of an alkaline material selected from the group consisting ofan alkali metal carbonate, sodium hydroxide, potassium hydroxide andtriethylamine.

23. The method of claim 22 wherein the alkaline material is an alkalimetal carbonate.

References Cited UNITED STATES PATENTS 3,361,652 1/1968 Korpuin et a1204-54 R 3,471,379 10/1969 Schoot et al 20454 R 2,552,920 5/1951 Allen204-54R FOREIGN PATENTS 652,405 12/1964 Belgium 204--54R 6501841 8/1966Netherlands 204-54'R FREDERICK C. EDMUNDSON, Primary Examiner US. Cl.X.R.

204-Dig. 2; 26072 UNITED STATES PATENT OFFTCE CETIFICATE or Patent No,694,329 Dated Sentemher 26 197? Inventor) Marcis M. Kampe It iscertified that error appears in the above' id'entifiedpatent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 32, --sulfate-- should be inserted m1 after "containing"and before "sul-"g line 69 Formula" should read --formula-- Column '5,line 29, "acetate" should be inserted after vinyl" and before"copolymers"."

Column 6, line 32, {'prinlay should read ---primary--. Column 7, linell, "suitably should read ----su:i.l:able--o Signed and sealed this 2kmday of April 1973.

(SEAL) Attest: V

ROBERTCOTTSCHALK] Commissioner of Patents EDWARD M. FLETCHER, J'R.Attssting Officer.

